Along most highways there are hazards that can be a substantial danger to drivers of automobiles if the automobiles leave the highway. To reduce the severity of accidents due to vehicles leaving a highway, guardrails are provided. The guardrails are installed such that the beam elements are in tension to aid in re-directive type impacts. Guardrails must be installed, however, such that the terminal end of the guardrail facing the flow of traffic is not a hazard. Early guardrails had no proper termination at the ends, and it was not uncommon for impacting vehicles to become impaled on the guardrail causing intense deceleration of the vehicle and severe injury to the occupants. In some reported cases, the guardrail penetrated directly, into the occupant compartment of the vehicle fatally injuring the occupants.
Upon recognition of the problem of proper guardrail termination, guardrail designs were developed that used box beams and W-beams that allow tapering of the end of the guardrail into the ground. Such designs eliminate any spearing effect. While these end treatments successfully removed the danger of the vehicle being penetrated in a head-on collision, it was discovered that these end treatments operate in a ramp-like fashion and may induce launching of the vehicle causing it to become airborne for a considerable distance with the possibility of roll over.
In search for better end treatments, improved energy absorbing end treatments for W-beam guardrail elements were developed. For example, an extruder terminal was developed and typically includes a bending structure that squeezes the guardrail into a flat plate and then bends it about a circular arc directed away from the impacting vehicle. Example extruder terminal products include the ET 2000™ and the ET-PLUS™ offered by Trinity Highway Products. Other extruder terminal products include the SKT 350™ and FLEAT 350™ offered by Road Systems, Inc.
All of these energy absorbing systems use a cable to connect the first w-beam guardrail segment to the first post in the system. The cable provides tension in the guardrail beam element for a redirective hit along the length-of-need portion of the guardrail. A number of cable releasing posts have also been developed for use in these terminals. The cable release posts are intended to release the cable anchor and, thus, release the tension in the system when the post is impacted in either of a forward (end-on) or reverse direction. Such systems are not able to remain in tension during end-on and reverse-direction type impacts.